Of course, “BEST” means different things to different people. But, I think the most versatile piece of useful equipment is a well-fitted pair of shoes. Shoes are the most important piece of equipment, because they support the body. Shoes create the foundation to help us all perform our best. Just remember the type of shoe you wear should match the type of activity you participate in. This is why basketball players wear high tops. Soccer player wear turf shoes. Tennis player wear tennis shoes. All shoes are designed with the end game in mind.
For example, running shoes are made to move forward, not side-to-side. I often see peoplecross training with running shoes on. This is a bad idea. There is little lateral support in a running shoe. A rolled ankle or a fall is waiting to happen. So, think carefully about what kind of activity you will participate in. If you wear your shoes for multiple activities get a pair of cross trainers.
Also, get your shoes fitted by a professional. It will make a difference. Be sure to take your old shoes with you. (A general rule of thumb is athletic shoes are good for about 500 miles. They do wear out!) The person fitting your new shoes should look at the way you walk barefoot and the wear patterns on the old shoes. This gives them clues as to the type of support you’ll need in your next pair. Also, try on several pairs. If you have been wearing a specific brand for years take the time to see how other companies are different or similar. You may be overlooking a great fitting shoe.